Decryption device

ABSTRACT

A decryption device includes: an internal-key storage section for storing an internal-key; a content-key storage section for storing a content-key; a determination section for determining whether or not a value of the content-key storage section in its initial state and a current value of the content-key storage section are different; and an operation section, the operation section including a first decrypting section which, when an encrypted content-key is input to the operation section, decrypts the encrypted content-key using the internal-key so as to obtain a content-key and stores the content-key in the content-key storage section, and a second decrypting section which, when an encrypted content is input to the operation section and the determination section determines that the value of the content-key storage section in its initial state and the current value of the content-key storage section are different, decrypts the encrypted content using the current value of the content-key storage section as a content-key so as to obtain a first output data and outputs the first output data to outside of the decryption device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a decryption device and anencryption/decryption device for encrypting/decrypting digital contents,such as music, image, video, game, etc.

2. Description of the Related Art

In recent years, along with the propagation of digital contents, such asmusic, image, video, game, etc., preventing fraudulent acts on suchdigital contents has been becoming more important for protecting rightsof a copyright owner, and a profit of a distributor, of such digitalcontents. The fraudulent acts include, for example, fraudulentobtainment of digital contents by means of interception ofcommunications, eavesdropping, pretending to be an authorized person,etc., and making an illegal copy from and illegal alteration to datareceived and stored in a recording medium. In order to prevent thesefraudulent acts, copyright protection techniques, such asencryption/authentication for determining whether or not it is anauthorized system or for data scrambling, are required.

In recent years, copyright protection techniques have been provided invarious consumer products. In general, a reproduction/recordingapparatus for digital contents achieves encrypting/decrypting processingusing an encryption/decryption device for performingencrypting/decrypting operations and a master control device forcontrolling the encryption/decryption device.

As described in the following, in the reproduction/recording apparatus,reproduction processing is performed using an encrypted content and anencrypted key (encrypted content-key) for decrypting the encryptedcontent.

In the first step, the master control device of thereproduction/recording apparatus reads data from a memory device(storage medium) storing encrypted contents and encrypted content-keys.An encrypted content-key read from the master control device is input toan encryption/decryption device. The encryption/decryption devicedecrypts this encrypted content-key using an internal-key, therebyobtaining a content-key. Then, the master control device inputs anencrypted content read from the memory device to theencryption/decryption device. The encryption/decryption device decryptsthe encrypted content using the obtained content-key and outputs thedecrypted content to the master control device. In this way, thereproduction processing for the encrypted content is performed.

Furthermore, in the reproduction/recording apparatus, recordingprocessing is performed as follows.

In the first step, the master control device issues a content-keygeneration instruction to the encryption/decryption device, whereby acontent-key used for encrypting a content is generated inside theencryption/decryption device. The encryption/decryption device encryptsthe content-key using the internal-key so as to obtain an encryptedcontent-key, and outputs the encrypted content-key to the master controldevice. Then, the master control device inputs a content to theencryption/decryption device. The encryption/decryption device encryptsthe content and outputs the encrypted content to the master controldevice. Thereafter, the master control device transfers the encryptedcontent and its encrypted content key to the memory device, whereby therecording processing is performed.

The encryption/decryption device operates in response to commands fromthe master control device. In the reproduction/recording apparatus, whenthe master control device is not tamper-resistant, theencryption/decryption device may be fraudulently operated. For example,it is possible to give the encryption/decryption device a command toencrypt or decrypt a content without providing a content-key in theencryption/decryption device.

In a conventional encryption/decryption device, in the case ofencrypting a content or decrypting an encrypted content, encrypting ordecrypting processing is initiated based on only a command supplied fromoutside. Therefore, when the encryption/decryption device receives acommand to encrypt a content or decrypt an encrypted content withoutproviding a content-key in the encryption/decryption device, theencryption/decryption device erroneously recognizes a value of a memoryregion in the encryption/decryption device, which is provided forstoring a content-key, as a content-key, and this value is used as acontent-key to encrypt a content or decrypt an encrypted content.

Such a value of the memory region is believed to be always the same whenthe encryption/decryption device is in the initial state e.g.,immediately after the encryption/decryption device is powered-on.Furthermore, encryption/decryption devices produced based on the samestandard operate in a similar manner. In the present specification, thevalue of the memory region in the encryption/decryption device, which isprovided for storing a content-key when the encryption/decryption deviceis in the initial state, e.g., immediately after theencryption/decryption device is powered-on, is referred to as an“initial content-key”.

By fraudulently operating the encryption/decryption device, it ispossible to encrypt a content or decrypt an encrypted content using theinitial content-key. A typical example of fraudulent acts achieved bysuch a fraudulent operation is now described in the following steps{circle around (1)}, {circle around (2)}, and {circle around (3)}:

-   {circle around (1)} A correlation between input data to and output    data from the decryption device which decrypts an encrypted content    using an initial content-key is examined. The output data is a    result of decrypting the input data using the initial content-key. A    correlation is examined for a number of pairs of input data and    output data, whereby the initial content-key and an algorithm for    decrypting processing are deciphered.-   {circle around (2)} When the initial content-key and the algorithm    for decrypting processing are deciphered at step {circle around    (1)}, an encryption device which encrypts any content using the    initial content-key can be fraudulently achieved. With such a    fraudulent encryption device, it is possible to encrypt a content    using the initial content-key and produce a fraudulent medium in    which the encrypted content is recorded.

Alternatively, with the encryption device which performs encryption withthe initial content-key, step {circle around (2)} can be achievedwithout step {circle around (1)}.

-   {circle around (3)} Data in the fraudulent medium produced at step    {circle around (2)} can be fraudulently decrypted by a decryption    device which decrypts an encrypted content using the initial    content-key. Such a decryption device which can fraudulently decrypt    an encrypted content is not limited to the decryption device used in    step {circle around (1)}. Any decryption device may be used so long    as it has the same initial content-key as that of the decryption    device used in step {circle around (1)}. Furthermore, the decryption    device does not need to be the same as the decryption device used in    step {circle around (2)}. Therefore, such a fraudulent act can    widely propagate without being limited within a single    encryption/decryption device.

Thus, in the conventional encryption/decryption device, when theencryption/decryption device is fraudulently operated such that acontent is encrypted or an encrypted content is decrypted using theinitial content-key, there is a possibility that the security of theencryption/decryption device may be deteriorated.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a decryption deviceincludes: an internal-key storage section for storing an internal-key; acontent-key storage section for storing a content-key; a determinationsection for determining whether or not a value of the content-keystorage section in its initial state and a current value of thecontent-key storage section are different; and an operation section, theoperation section including a first decrypting section which, when anencrypted content-key is input to the operation section, decrypts theencrypted content-key using the internal-key so as to obtain acontent-key and stores the content-key in the content-key storagesection, and a second decrypting section which, when an encryptedcontent is input to the operation section and the determination sectiondetermines that the value of the content-key storage section in itsinitial state and the current value of the content-key storage sectionare different, decrypts the encrypted content using the current value ofthe content-key storage section as a content-key so as to obtain a firstoutput data and outputs the first output data to outside of thedecryption device.

In one embodiment of the present invention, the decryption devicefurther includes a content-key generation section which generates acontent-key for encrypting a content based on random numbers and storesthe generated content-key in the content-key storage section, whereinthe operation section further includes a first encrypting section whichencrypts the content-key for encrypting a content so as to obtain anencrypted content-key and outputs the encrypted content-key to outsideof the decryption device, and a second encrypting section which, when acontent is input to the operation section and the determination sectiondetermines that the value of the content-key storage section in itsinitial state and the current value of the content-key storage sectionare different, encrypts the content using the current value of thecontent-key storage section as a content-key so as to obtain a secondoutput data and outputs the second output data to outside of thedecryption device.

In another embodiment of the present invention, the decryption devicefurther includes a mutual authentication section for determining whetheror not a mutual authentication has been made between the mutualauthentication section and a storage device which is located outside thedecryption device and stores the encrypted content-key, wherein thesecond decrypting section decrypts the encrypted content when the mutualauthentication section determines that the mutual authentication hasbeen made.

In still another embodiment of the present invention, the internal-keystorage section stores a plurality of internal-keys; and theinternal-key storage section selects one of the plurality ofinternal-keys as the internal-key based on internal-key selectioninformation input from outside the decryption device to the decryptiondevice.

Now, functions of the present invention are described.

A decryption device according to the present invention has adetermination section for determining whether or not a value of acontent-key storage section in its initial state and a current value ofthe content-key storage section are different. When an encrypted contentis input to an operation section, and a value of the content-key storagesection in its initial state and the determination section determinesthat a current value of the content-key storage section are different, asecond decrypting section included in the operation section performsdecrypting processing for the encrypted content. With such anarrangement, the decrypting processing for the encrypted content isprevented from being performed while the value of the content-keystorage section is in the initial state. That is, the decryptingprocessing for the encrypted content is prevented from being performedusing an initial content-key. Thus, the security of the decryptiondevice is improved.

When a decryption device according to the present invention furtherincludes a second encrypting section, the decryption device functions asan encryption/decryption device. When a content is input to an operationsection, and a determination section determines that a value of thecontent-key storage section in its initial state and a current value ofthe content-key storage section are different, the second encryptingsection encrypts the content using the current value of the content-keystorage section as a content-key so as to obtain a second output data,and outputs the first output data to outside of theencryption/decryption device. With such an arrangement, the encryptingprocessing for the content is prevented from being performed while thevalue of the content-key storage section is in the initial state. Thatis, the encrypting processing for the content is prevented from beingperformed using an initial content-key. Thus, the security of theencryption/decryption device is improved.

Thus, the invention described herein makes possible the advantage ofproviding an encryption/decryption device with improved security thatcan prevent a fraudulent operation in which a content is encrypted or anencrypted content is decrypted using the initial content-key.

This and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a structure of a decryption device 101according to embodiment 1 of the present invention.

FIG. 2 is a block diagram showing an exemplary internal structure of thedecrypting operation section 103.

FIG. 3 shows an exemplary internal structure of the state transitionmanagement section 111 of FIG. 1.

FIG. 4 is a block diagram showing a structure of anencryption/decryption device 201 according to embodiment 2 of thepresent invention.

FIG. 5 is a block diagram showing an exemplary internal structure of theencrypting/decrypting operation section 203.

FIG. 6 is a block diagram showing a structure of a decryption device 401according to embodiment 3 of the present invention.

FIG. 7 is a block diagram showing a structure of a decryption device 301which includes a content-key verification section 315 in addition to thecomponents of the decryption device 101 according to embodiment 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings. In the present specification, a “decryptiondevice” is a device which has a function for decrypting encrypted data(decrypting function); and an “encryption/decryption device” is a devicewhich has both the decrypting function and a function for encryptingdata (encryption function). Thus, in the present specification, aconcept of decryption devices includes encryption/decryption devices.

Embodiment 1

FIG. 1 shows a structure of a decryption device 101 according toembodiment 1 of the present invention. The decryption device 101decrypts input data 102 based on information from a master device 100which acts as a host (the input data 102, internal-key selectioninformation 106, and processing mode information 108).

The decryption device 101 is used with the master device 100, and ismounted on a reproduction/recording apparatus (not shown). The masterdevice 100 has a function for reading encrypted contents and encryptedcontent-keys from a predetermined region 412 in a memory device 316.

The memory device 316 may be any recording medium. In the illustratedembodiment, the memory device 316 is a semiconductor storage medium.

The decryption device 101 includes an internal-key storage section 105,a state transition management section 111, a processing mode selectionsection 109, a decrypting operation section 103, and a content-keystorage section 107.

The internal-key storage section 105 stores an internal-key inherent tothe decryption device 101. The internal-key storage section 105 isprovided in a region of the decryption device 101 which is inaccessiblefrom outside. The internal-key storage section 105 stores theinternal-key inherent to the decryption device 101 in a hard-wiredmanner, or in a ROM or a non-volatile memory. The internal-key storagesection 105 may store a plurality of internal-keys. In the case wherethe internal-key storage section 105 stores a plurality ofinternal-keys, one of the plurality of internal-keys is selected basedon the internal-key selection information 106 input from the masterdevice 100.

The content-key storage section 107 stores content-keys for decryptingencrypted contents.

The state transition management section 111 determines whether or not acontent-key (a content-key for decrypting encrypted contents) is storedin the content-key storage section 107. In particular, the statetransition management section 111 functions as a determination sectionfor determining whether or not a value of the content-key storagesection 107 in its initial state and a current value of the content-keystorage section 107 are different. When the current value of thecontent-key storage section 107 is the same as the value of thecontent-key storage section 107 in its initial state, the content-keystorage section 107 does not include any content-key, i.e., the statetransition management section 111 determines that the value of thecontent-key storage section 107 is an initial content-key. The statetransition management section 111 transmits to the decrypting operationsection 103 determination information 1101 which indicates whether ornot the value of the content-key storage section 107 in its initialstate and a current value of the content-key storage section 107 aredifferent.

The processing mode selection section 109 interprets the processing modeinformation 108 input from the master device 100. The processing modeinformation 108 is a command supplied from the master device 100 to thedecryption device 101. The decryption device 101 performs two types ofdecrypting processing, i.e., decrypting processing for an encryptedcontent-key and decrypting processing for an encrypted content. Thus,the processing mode information 108 supplied as a command from themaster device 100 to the decryption device 101 indicates whichdecrypting processing should be performed by the decryption device 101.The processing mode selection section 109 outputs control information1102 to the decrypting operation section 103 based on the result of theinterpretation of the processing mode information 108.

In this way, the processing mode selection section 109 interprets theprocessing mode information 108 and controls the decrypting operationsection 103 based on the result of the interpretation. However, when thedecrypting operation section 103 is directly controlled by theprocessing mode information 108 supplied from the master device 100, theprocessing mode selection section 109 can be omitted.

The decrypting operation section (operation section) 103 performs twotypes of decrypting processing, i.e., decrypting processing for anencrypted content-key and decrypting processing for an encryptedcontent.

FIG. 2 schematically shows an exemplary internal structure of thedecrypting operation section 103.

The decrypting operation section 103 includes a first decrypting section1201 for decrypting an encrypted content-key and a second decryptingsection 1202 for decrypting an encrypted content.

The first decrypting section 1201 is activated when the processing modeinformation 108 from the master device 100 (FIG. 1) indicates thedecrypting processing for an encrypted content-key. When an encryptedcontent-key is input as input data 102 from the master device 100 to thefirst decrypting section 1201, the first decrypting section 1201decrypts the encrypted content-key using an internal-key stored in theinternal-key storage section 105. The decrypted data is stored as acontent-key in the content-key storage section 107.

The second decrypting section 1202 is activated when the processing modeinformation 108 from the master device 100 (FIG. 1) indicates thedecrypting processing for an encrypted content. When an encryptedcontent (data including encrypted digital content such as music, image,video, game, etc.) is input as input data 102 from the master device 100to the second decrypting section 1202, and the determination information1101 output from the state transition management section 111 indicatesthat “the value of the content-key storage section 107 in its initialstate and a current value of the content-key storage section 107 aredifferent”, the second decrypting section 1202 decrypts the encryptedcontent using the value of the content-key storage section 107 as acontent-key. The decrypted data (first output data) is output to themaster device 100 as output data 104. In this example, the first outputdata is a content obtained by decrypting the encrypted content.

In this way, the second decrypting section 1202 performs the decryptingprocessing for an encrypted content after it has been confirmed that“the value of the content-key storage section 107 in its initial stateand a current value of the content-key storage section 107 aredifferent”. With such an arrangement, even when the master device 100 isnot tamper-resistant (hence, even when fraudulent input data andprocessing mode information are input to the decryption device 101through fraudulent routes 102 a and 108 a), the decrypting processingfor an encrypted content is prevented from being performed while thecontent-key storage section 107 is in the initial state. That is, thedecrypting processing for an encrypted content is prevented from beingperformed using an initial content-key. Thus, steps {circle around (1)}and {circle around (3)} in the above-described typical example offraudulent acts are prevented from being performed and, accordingly, adecryption device with improved security is achieved.

The decryption device 101 may be, for example, an ASIC (ApplicationSpecified IC). The master device 100 may be, for example, an MPU(Microprocessor Unit). Thus, the decryption device 101 may be producedas a single semiconductor package.

Any encryption/decryption algorithm may be employed for the decryptingprocessing performed in the first decrypting section 1201 and the seconddecrypting section 1202 of the decrypting operation section 103. Forexample, the DES (Data Encryption Standard) may be employed.Furthermore, the length of an internal-key and a content-key may be anybit. For example, it may be 56 bits.

The internal structure of the decrypting operation section 103 is notlimited to the internal structure shown in FIG. 2. The first decryptingsection 1201 and the second decrypting section 1202 may have the samestructure. Thus, the first decrypting section 1201 and the seconddecrypting section 1202 may be provided as a single decrypting section.

FIG. 3 shows an exemplary internal structure of the state transitionmanagement section 111 of FIG. 1. The state transition managementsection 111 is connected to the content-key storage section 107. Thestate transition management section 111 includes a register 1301 and acomparator 1302. The register 1301 holds the value of an input 1303 (thevalue of the content-key storage section 107) at the time when a pulsesignal is input to a latch input 1305. The comparator 1302 compares anoutput 1304 of the register 1301 and the input 1303 (the value of thecontent-key storage section 107) so as to output a comparison result1306. The comparison result 1306 is input to the decrypting operationsection 103 (FIG. 1) as the determination information 1101.

The latch input 1305 of the register 1301 receives a POR (Power OnReset) signal. The POR signal is a signal which pulses only onceimmediately after power-on. A power supply used for the power-on may be,for example, a power supply for the decryption device 101 or a powersupply for a reproduction/recording apparatus (not shown) on which thedecryption device 101 is mounted. After the power-on, a value of thecontent-key storage section 107 immediately after the power-on is heldin the register 1301. Accordingly, the comparator 1302 compares thevalue of the content-key storage section 107 immediately after thepower-on and a current value of the content-key storage section 107.When these values are equal, the output (comparison result) 1306 of thecomparator 1302 is “0”; otherwise, the output 1306 of the comparator1302 is non-zero.

In this way, the state transition management section 111 can determinewhether or not the value of the content-key storage section 107 in itsinitial state and a current value of the content-key storage section 107are different. In the above example, the initial state is a stateimmediately after the power-on, but according to the present invention,the initial state is not limited thereto. For example, the initial statemay be a state immediately after the whole decryption device 101 isreset. A pulse signal is input to the latch input 1305 of the statetransition management section 111 immediately after any initial state,whereby the state transition management section 111 can determinewhether or not the value of the content-key storage section 107 in itsinitial state and a current value of the content-key storage section 107are different.

The structure of the state transition management section 111 is notlimited to the structure shown in FIG. 3. The state transitionmanagement section 111 may have any structure so long as it has afunction for determining whether or not the value of the content-keystorage section 107 in its initial state and a current value of thecontent-key storage section 107 are different.

Embodiment 2

FIG. 4 shows a structure of an encryption/decryption device (decryptiondevice) 201 according to embodiment 2 of the present invention. Theencryption/decryption device 201 includes an encrypting/decryptingoperation section 203 in place of the decrypting operation section 103of the decryption device 101. Furthermore, the encryption/decryptiondevice 201 includes a content-key generation section 213. In FIG. 4,like elements are indicated by like reference numerals used in FIG. 1,and detailed descriptions thereof are omitted.

The encryption/decryption device 201 is used with a master device 200,and is mounted on a reproduction/recording apparatus (not shown). Themaster device 200 has a function for reading/writing encrypted contentsand encrypted content-keys from/in a predetermined region 412 in amemory device 316.

The encrypting/decrypting device 201 performs four types of processing,i.e., decrypting processing for an encrypted content-key, decryptingprocessing for an encrypted content, generation processing forgenerating a content-key, and encrypting processing for encryptingcontents. Thus, a processing mode information 108 supplied as a commandfrom the master device 200 to the encryption/decryption device 201indicates which processing should be performed by theencryption/decryption device 201.

When the processing mode information 108 indicates the decryptingprocessing for an encrypted content-key, the content-key generationsection 213 generates at random a content-key for encrypting contents,and the generated content-key is stored in the content-key storagesection 107. For example, the content-key for encrypting contents isgenerated based on random numbers. The random numbers are generated bygenerating integers at random using a clock counter, for example.

FIG. 5 shows an exemplary internal structure of theencrypting/decrypting operation section 203. The encrypting/decryptingoperation section (operation section) 203 includes, in addition to thecomponents of the decrypting operation section 103 shown in FIG. 2, afirst encrypting section 1501 for encrypting content-keys and a secondencrypting section 1502 for encrypting contents. In FIG. 5, likeelements are indicated by like reference numerals used in FIG. 2, anddetailed descriptions thereof are omitted.

The first encrypting section 1501 is activated when the processing modeinformation 108 from the master device 200 (FIG. 4) indicates theencrypting processing for a content-key. When the processing modeinformation 108 indicates the encrypting processing for a content-key,the content-key generation section 213 (FIG. 4) generates a content-keyfor encrypting contents based on the random numbers as described above.The first encrypting section 1501 encrypts the content-key forencrypting contents using an internal-key stored in internal-key storagesection 105, thereby obtaining an encrypted content-key (secondencrypted content-key). This encrypted content-key is output as outputdata 104 to the master device 200 located outside theencryption/decryption device 201.

The second encrypting section 1502 is activated when the processing modeinformation 108 from the master device 200 (FIG. 4) indicates theencrypting processing for a content. When the content is input as inputdata 102 from the master device 200 (FIG. 4) to the second encryptingsection 1502, and the determination information 1101 output from thestate transition management section 111 indicates that “the value of thecontent-key storage section 107 in its initial state and a current valueof the content-key storage section 107 are different”, the secondencrypting section 1502 encrypts the content using the value of thecontent-key storage section 107 as a content-key. The encrypted data(second output data) is output to the master device 200 as output data104. In this example, the second output data is an encrypted contentobtained by encrypting the content.

In this way, the second encrypting section 1502 performs the encryptingprocessing for a content after it has confirmed that “the value of thecontent-key storage section 107 in its initial state and a current valueof the content-key storage section 107 are different”. With such anarrangement, even when the master device 200 is not tamper-resistant,the encrypting processing for a content is prevented from beingperformed while the content-key storage section 107 is in the initialstate. That is, the encrypting processing for a content is preventedfrom being performed using an initial content-key. Thus, step {circlearound (2)} in the above-described typical example of fraudulent acts isprevented from being performed and, accordingly, a decryption devicewith improved security is achieved.

The encryption/decryption device 201 may be, for example, an ASIC(Application Specified IC). The master device 200 may be, for example,an MPU (Microprocessor Unit). Therefore, the encryption/decryptiondevice 201 may be produced as a single semiconductor package.

Any encryption/decryption algorithm may be employed for encryptingprocessing performed in the first encrypting section 1501 and the secondencrypting section 1502 of the encrypting/decrypting operation section203. For example, the DES (Data Encryption Standard) may be employed.

The internal structure of the encrypting/decrypting operation section203 is not limited to the internal structure shown in FIG. 5. The firstencrypting section 1501 and the second encrypting section 1502 may havethe same structure. Thus, the first encrypting section 1501 and thesecond encrypting section 1502 may be provided as a single decryptingsection.

Embodiment 3

FIG. 6 shows a structure of a decryption device 401 according toembodiment 3 of the present invention. The decryption device 401includes a mutual authentication section 417 in addition to thecomponents of the decryption device 101 shown in FIG. 1. In FIG. 6, likeelements are indicated by like reference numerals used in FIG. 1, anddetailed descriptions thereof are omitted.

The decryption device 401 is used with the master device 400, and ismounted on a reproduction/recording apparatus (not shown). The masterdevice 400 has a function for reading encrypted contents and encryptedcontent-keys from a predetermined region 412 in a memory device 416.

The memory device 416 may be any recording medium. In the illustratedembodiment, the memory device 416 is a semiconductor storage medium. Thememory device 416 has a mutual authentication section 414.

A mutual authentication is made between the mutual authenticationsection 414 of the memory device 416 and the mutual authenticationsection 417 of the decryption device 401. Any mutual authenticationprocedure may be used for the mutual authentication between the mutualauthentication sections 414 and 417. A mutual authentication procedureknown as a challenge-response system is one example of the mutualauthentication procedure used between the mutual authentication sections414 and 417.

The state transition management section 111 determines whether or notthe mutual authentication has been made. When the state transitionmanagement section 111 determines that the mutual authentication hasbeen made, the second decrypting section 1202 (FIG. 2) of the decryptingoperation section 103 decrypts an encrypted content.

In the example shown in FIG. 6, the state transition management section111 determines whether or not the mutual authentication has been made.However, according to the present invention, the mutual authenticationsection 417 may carry out the determination.

In the decryption device 401 according to the present invention, thevalidity of the memory device 416 storing an encrypted content-key isconfirmed. Thus, it is possible to more securely prevent the decryptingprocessing for contents from being fraudulently operated.

Furthermore, in the decryption device 401 according to the presentinvention, reading from a “fraudulent medium” (memory device), as instep {circle around (3)} of the above-described typical example offraudulent acts, is prevented in a more secure manner. Accordingly, thesecurity of the decryption device 401 is improved.

According to the present invention, the encryption/decryption device 201shown in FIG. 4 may include the mutual authentication section 417 shownin FIG. 6. In this case, the second encrypting section 1502 (FIG. 5) ofthe encrypting/decrypting operation section 203 performs encryptingprocessing for a content when the mutual authentication has been made,whereby the security of the decryption device 201 is improved.

Furthermore, the decryption device (or encryption/decryption device)according to each of embodiments 1-3 may include a content-keyverification section which contains a verification pattern and whichdetermines whether a content-key is valid or not.

FIG. 7 shows a structure of a decryption device 301 including acontent-key verification section 315 in addition to the components ofthe decryption device 101 (FIG. 1) according to embodiment 1.

The decrypting operation section 103 decrypts an encrypted verificationpattern using a value of the content-key storage section 107 as acontent-key, thereby obtaining a decrypted data. If this decrypted datamatches a verification pattern stored in the content-key verificationsection 315, it is determined that the value of the content-key storagesection 107 is a valid content-key.

The second decrypting section 1202 of the decrypting operation section103 (FIG. 2) performs decrypting processing for contents only when thevalue of the content-key storage section 107 is a valid content-key.With such an arrangement, an invalid content-key (e.g., an initialcontent-key) is prevented from being used for decrypting contents.

A decryption device according to the present invention has adetermination section for determining whether or not a value of acontent-key storage section in its initial state and a current value ofthe content-key storage section are different. When an encrypted contentis input to an operation section, and a value of the content-key storagesection in its initial state and the determination section determinesthat a current value of the content-key storage section are different, asecond decrypting section included in the operation section performsdecrypting processing for the encrypted content. With such anarrangement, the decrypting processing for the encrypted content isprevented from being performed while the value of the content-keystorage section is in the initial state. That is, the decryptingprocessing for the encrypted content is prevented from being performedusing an initial content-key. Thus, the security of the decryptiondevice is improved.

When a decryption device according to the present invention furtherincludes a second encrypting section, the decryption device functions asan encryption/decryption device. When a content is input to an operationsection, and a determination section determines that a value of thecontent-key storage section in its initial state and a current value ofthe content-key storage section are different, the second encryptingsection encrypts the content using the current value of the content-keystorage section as a content-key so as to obtain a second output data,and outputs the first output data to outside of theencryption/decryption device. With such an arrangement, the encryptingprocessing for the content is prevented from being performed while thevalue of the content-key storage section is in the initial state. Thatis, the encrypting processing for the content is prevented from beingperformed using an initial content-key. Thus, the security of theencryption/decryption device is improved.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

1. A decryption device comprising: an internal-key storage sectionadapted to store an internal-key; a content-key storage section adaptedto store content-keys; a determination section adapted to determinewhether or not a value of the content-key storage section in an initialstate and a current value of the content-key storage section aredifferent; and an operation section, the operation section including: afirst decrypting section adapted to, when an encrypted content-key isinput to the operation section, decrypt the encrypted content-key usingthe internal-key so as to obtain a content-key and store the content-keyin the content-key storage section, and a second decrypting sectionadapted to, when an encrypted content is input to the operation sectionand the determination section determines that the value of thecontent-key storage section in the initial state and the current valueof the content-key storage section are different, decrypt the encryptedcontent using the current value of the content-key storage section asthe content-key so as to obtain a first output data and output the firstoutput data to outside of the decryption device, wherein thedetermination section comprises a register for storing a value of thecontent-key storage section at the time that said register receives aPower On Reset (POR) signal, and wherein the POR signal is a signalwhich pulses only once immediately after power-on or immediately afterreset, so that the content key storage section is in the initial stateimmediately after a corresponding power-on or reset of the decryptiondevice.
 2. A decryption device according to claim 1, further comprisinga mutual authentication section adapted to determine whether or not amutual authentication has been made between the mutual authenticationsection and a storage device which is located outside the decryptiondevice, and store the encrypted content-key being stored in the storagedevice; wherein the second decrypting section is adapted to decrypt theencrypted content when the mutual authentication section determines thatthe mutual authentication has been made.
 3. A decryption deviceaccording to claim 1, wherein: the internal-key storage section isadapted to store a plurality of internal-keys; and the internal-keystorage section is adapted to select one of the plurality ofinternal-keys as the internal-key based on internal-key selectioninformation input from outside the decryption device to the decryptiondevice.
 4. A decryption device according to claim 1, wherein: the seconddecrypting section is further adapted to prevent decryption of theencrypted content when the determination section determines that thevalue of the content-key storage section in the initial state and thecurrent value of the content-key storage section are the same.
 5. Amethod for decrypting encrypted content in a decryption device includingan internal-key storage section and a content-key storage section, themethod comprising: storing an internal-key in the internal-key storagesection; storing content-keys in the content-key storage section;determining whether or not a value of the content-key storage section inan initial state and a current value of the content-key storage sectionare different; and decrypting an encrypted content-key provided to thedecryption device by using the internal-key so as to obtain acontent-key and storing the content-key in the content-key storagesection; and when it is determined that the value of the content-keystorage section in the initial state and the current value of thecontent-key storage section are different, decrypting the encryptedcontent using the current value of the content-key storage section asthe content-key so as to obtain a first output data and outputting thefirst output data to outside of the decryption device, wherein, for thedetermination step, a register stores a value of the content-key storageat the time that said register receives a Power On Reset (POR) signal,and wherein the POR signal is a signal which pulses only onceimmediately after power-on or immediately after reset, so that thecontent key storage section is in the initial state immediately after acorresponding power-on or reset of the decryption device.
 6. A methodaccording to claim 5, further comprising: storing a plurality ofinternal-keys in the internal-key storage section; and selecting one ofthe plurality of internal-keys as the internal-key based on internal-keyselection information input from outside the decryption device to thedecryption device.
 7. A method according to claim 5, further comprising:preventing decryption of the encrypted content when it is determinedthat the value of the content-key storage section in the initial stateand the current value of the content-key storage section are the same.